Various packet-switched voice communications systems have been developed exclusively for communications within a packet-switched computer network, such as the Internet. These systems include software running on two computers which communicate with each other using a client-server model. A user speaks into a microphone connected to a source computer. The user's voice is digitized and is placed into data packets by a client process on the source computer. The packets of voice data are then sent over the packet-switched network to a server process on the destination computer. The server process extracts the voice data from the packet, converts it to analog format and sends the analog signal to a speaker. Full-duplex communication is provided by having each computer run both a client process for sending and a server process for receiving. An example of such a software package is Microsoft Corporation's NetMeeting Software.
One drawback to these types of systems is that communications are strictly limited to other computer users on the packet-switched computer network. Since the voice is digitized and placed into packets which are sent one at a time over the network, only computers which are interconnected to the same network and use the same protocols have the ability to communicate with each other. Packet-switched networks are referred to as connectionless networks, since each individual packet may take a different route through the network on its way from a source to a destination computer. The end user perceives a seamless connection referred to as a virtual circuit.
By contrast, circuit-switched networks, such as the Public Switched Telephone Network (PSTN), use a vast network of interconnected switching centers known as the Public Switched Telephone Network (PSTN). On these networks. special signaling is used to set up a dedicated circuit connection for the duration of a telephone call. Since the same physical circuit is used to send and receive voice signals during the entire call, these networks are referred to as connection oriented networks.
Interconnecting circuit and packet-switched networks presents a problem. Since the two types of networks use different signaling and protocols at various data communications layers, the communication techniques of these networks are incompatible. Wiring that is commonly used for packet-switched networks, such as Ethernet cable, is incompatible with circuit-switched networks, which commonly use twisted pair cabling.
Accordingly, there is a need for a method and apparatus for interconnecting voice connections between circuit-switched and packet-switched networks.